However, this argument does not rule out the possibility that there could be some kind of generalized `quasi-causal' description which might play a similar kind of functional role to a traditional causal model in the context of phenomena which fail to exhibit causal order. Indeed, insofar as these phenomena are to some degree under the control of macroscopic agents, it must surely be possible to arrive at a description of them which characterises the way in which they can be used to achieve practical goals and purposes, just as a traditional causal description would do. And this is exactly what is achieved by the formalism of quantum causal models, as presented in section . For quantum causal models do not appear to be attempting to describe an `underlying reality' for quantum mechanics, but rather the reverse - they provide a `top-down' description of the laboratory procedures that are implemented on the relevant systems, so for example ref [1]} suggests that quantum causal models are suitable for the case where `one typically does not have a direct description of the causal mechanisms, but rather only a very coarse-grained description of them in terms of laboratory procedures that are implemented on the relevant systems' and ref [2]} notes that if this methodology is applied to characterise a quantum circuit, it will often simply yield the connectivity graph representing the way the gates are literally wired together in the laboratoryOr it may yield a subgraph of this connectivity graph, because there may turn out to be nodes which do not influence one another even though they are physically connected.. Essentially, the quantum causal structure provides a set of instructions for the minimum possible laboratory operations which would be needed to produce the desired effects. Thus these models serve a similar function to causal descriptions in that they show us how to construct quantum circuits which are suitable to achieve various goals, so from the functional point of view the idea that these models have a claim to be thought of as quasi-causal seems very reasonable.
